(1) Field of the Invention
The present invention relates to ceramic value seats for use as valve-contacting faces in engine cylinder heads.
(2) Related Art Statement
Since the valve seats used in internal combustion engines are exposed to high temperatures and worn due to repeated loading of the valves, it has been attempted to use heat resisting alloys or ceramics for valve seat materials.
However, it has become difficult for valve seats made of heat resisting alloys to satisfy operating conditions at high temperatures and high pressures which have been severer year by year and to bear wearing conditions due to repeated loading, and mean time between overhaulings unfavorably decreases.
Although the valve seats made of ceramic materials can solve the above-mentioned shortcomings of the valve seats made of the heat resisting alloys, a stress concentration, at edge portions of the valve-contacting face of the valve seat, is likely to occur. Consequently, the ceramic valve seats have the drawbacks that the valve seats crack or fracture in an extreme case.